Some counties and cities are not officially designated by the OMB as members of this metropolitan area, but still consider themselves members anyway.[citation needed][clarification needed] This is mostly due to their proximity to the area, the size of their commuter population, and by the influence of local broadcasting stations. The population of the entire Baltimore–Washington Metroplex as of the Census Bureau's 2012 Population Estimates is 9,331,587.[4][5][6][7][8][9][10] The most populous city is Washington, DC, with a population of 646,449.[11] The most populous county is Fairfax County, Virginia, with a population exceeding 1.1 million.

The counties and independent cities and their groupings that comprise the metropolitan area are listed below with their 2012 population estimates. Central counties/cities (designated as such by OMB) for each MSA are shown in italics.

The Baltimore Metropolitan Council is the equivalent organization for the Baltimore portion of the combined Baltimore–Washington metropolitan area.[14] The BMC, which was created in 1992 as the successor to the Regional Planning Council and Baltimore Regional Council of Governments, consists of the Baltimore region's elected executives, representing Baltimore City and Anne Arundel, Baltimore, Carroll, Harford and Howard counties.[15]